A transducer is a device that converts energy from one form into another form. One particular class of transducers provides an electrical output signal in response to an acoustic input, or an acoustic output in response to an electrical input. In the field of underwater acoustics, a transducer that is designed to accomplish the former function—produce an electrical output in response to an acoustic input—is called a “hydrophone.” A transducer that generates an acoustic output signal in response to an electrical input is called a “projector.” Hydrophones and projectors are commonly used for underwater ranging and detection, velocity measuring, imaging, etc.; that is, sonar.
Sonar arrays typically include multiple transducers and can take a variety of forms. In some arrays, such as the one depicted in FIG. 1, multiple transducers 102 are precisely spaced apart in a linear array 100 and towed behind a ship or submarine (not depicted). In some other arrays, such as are sometimes used in submarines, multiple transducers 102 are arranged in 2d arrays 200 (e.g., square, rectangular, etc.) and installed in the hull 206 of the submarine (see, FIG. 2). In certain sonar arrays, some of the transducers function as projectors while others function as hydrophones. In some other arrays, all transducers function as hydrophones, and in still other sonar arrays, all transducers function as projectors and hydrophones.
In active sonar arrays, such as sonar arrays 100 and 200, transducers that are operating as projectors convert electrical energy that is generated by sonar transmitter 104 into sound waves. The sound waves are launched into the surrounding water. The sound waves, which collectively propagate as an acoustic beam, travel through a region of the water in a beam to perform the intended sonar function.
By appropriately controlling phase and amplitude of the electrical signals that are applied to individual projectors in the sonar array, one or more acoustic beams having appropriate shapes can be formed and steered to scan a particular region. The region that is acoustically imaged is referred to as the “ensonification field.” Objects that are located within the ensonification field reflect or scatter the acoustic beam(s), thereby generating return sound signals or “echo.”
The echo is received by transducers 102 in the array that are operating as hydrophones. The hydrophones convert the echo to electrical signals, which are transmitted to sonar receiver 105. The electrical signals, which are representative of the echo, are then processed and the results are displayed in a form that is useful by sonar personnel for identifying, locating, etc., the ensonified objects.
Sometimes, the performance of a sonar array degrades over time. The degradation can result from partial or complete failure of one or more of the transducers (hydrophones) in the array. Historically, “electrical tone application” or “conductivity” tests have been used to identify malfunctioning transducers. These tests are limited, however, in their ability to identify partial malfunctions. Furthermore, these tests are generally not capable of quantifying the extent of the malfunction or predicting its affect on array performance. Once a malfunctioning transducer is identified via these techniques, it is either electronically removed from the array or physically replaced. But it might take an extended period of time before an opportunity to replace a transducer arises. And electronically removing one or more transducer(s) from a sonar array might reduce the capabilities (e.g., power, sensitivity, etc.) of the array.
Furthermore, on occasion, sonar arrays comprising newly-manufactured transducers that have passed all standard factory test requirements do not perform as expected. Since the transducers have passed standard factory tests, and short of an autopsy, there is often little that can be done to determine which of the transducers in the array are faulty. Depending upon the extent of the performance deficit, the array is either deployed with compromised performance or replaced before deployment with a concomitant delay in mission readiness.
It would, therefore, be desirable to have a new diagnostic method and system that exhibits one or more of the following attributes:                Is more reliable and capable than prior-art techniques at identifying partially malfunctioning transducers.        Is able to quantify the effect that a malfunctioning transducer will have on the performance of a transducer array.        Provides data that can be used by processing electronics as a “calibration factor” to correct for the degradation of one or more transducers in the array.        Provides data that can be used to yield the best performance from a given group of transducers by selectively positioning the “best” transducers at the most critical positions in the array.        Complements or replaces standard factory-acceptance tests for transducers.        